Hi! I'm new here and finding my way in the world of acoustic insulation as in the process of insulating a garage/outbuilding to make it a suitable percussion practice space. I would be so grateful if anyone could offer thoughts/experience on the following.

We are trying to keep the costs reasonable and working with a general builder friend on this project. Our priority is to reduce sound transmission to the extent where I won’t annoy the neighbours and also won’t be constantly advertising all the valuable gear I’m keeping in there! We are talking drum kit, timpani, xylophone etc… high and low frequencies. I don’t have any technical acoustic figures we are aiming for, but proximity of neighbours is as you would expect for a London street - houses about 5m away on two sides and a c.10m gap between our outbuilding and our next-door neighbours (not a party wall but the roof is joined with ridge tiles). Nobody lives in next door’s outbuilding but it’s the sort of area where that could be a possibility in future…legally or otherwise!

The original outbuilding is essentially like a freestanding garage, brick construction on the outside with small cavity (empty or inconsistently filled we think) and a breeze-block inner wall, which has a layer of 15mm acoustic plasterboard attached to it. It has a pitched roof with rafters infilled with rockwool and 15mm acoustic plasterboard attached directly to the rafters.

We now have a completely freestanding studwork RWAR structure inside the building. It’s about 5mx4m floor area. This has been built on a floating floor and all studwork is infilled with 100mm rockwool and lined with 5mm of mass loaded vinyl. It's due to be finished with plasterboard in the next couple of days and I'm not sure whether to get the boards mounted straight onto the stud work of walls and ceiling, or use resilient channels. The current level of insulation when we've tested it is definitely headed in the right direction in terms of reducing sound transmission, and I'm not sure whether using resilient channel is enough of a necessity to warrant the extra expense and loss of space inside the room, but I need to make a quick decision. There seem to be a number of different opinions about the merits of using RC on an already decoupled structure and it's hard to discern who is just out to sell me stuff!

Then there are the different type of RCs…Some that mount onto a rubber clip system (such as Isomax), presumably most effective, but £££, and I’m not sure we’re far enough off the desired result in terms of sound reduction to justify the cost. More basic RCs that mount directly onto studs could be an option but I'm not clear if they are likely to make a significant difference to be worth the bother.

Would love to hear from anyone who has a pearl of wisdom! Very many thanks.

As you already have a floating structure I'd say that you won't need resilient bars. However, a single layer of plasterboard my not be sufficient. I'd suggest going for 19mm plasterboard planks next to the studs with a further layer of 12mm acoustic plasterboard. Some people would recommend adding another layer of 15mm acoustic plasterboard on top. Acoustic plasterboard is more dense than standard plasterboard but not hugely more expensive. In my studio I've used a layer of Green Glue between the plasterboard layers which gives a little compliance. I live in a quiet neighbourhood and drums have never been a problem in my studio.

The most important things to watch out for are the weak points - doors, windows and ventilation. If these aren't constructed correctly you'll negate all your hard work in making the walls soundproof.

The problem with General Builders is that they work in a culture where it is the norm to cut corners. They really do have to work the margins to make a profit, so it is very tempting for them to use, for example, 10 sheets of x where 10 and a half sheets are required to do the job.

That is a hard habit to break.

Sound proofing only works if it is done right, so you need to take James's advice very seriously. If your builder is a genuine friend you need to make it clear that he needs to price the job honestly and resist the temptation to cut corners. And, in return, you need to make it clear that you are prepared to pay a fair price for a job done correctly.

Ideally, you should be considering getting a qualified acoustician to plan the work AND manage the building work to ensure corners aren't cut. Sadly, it is very easy to spend thousands and see no benefts because your builder doesn't understand real sound proofing.

James is right here, i've just done a similar construction albeit on a smaller scale.

Floated the entire stud frame, attached the ceiling joists to the frame and ensured that no part of the frame touches the outer block construction. Infilled with Flexislab, then 2 layers of 12.5 mm soundbloc with green glue (2 tubes per sheet) between them, non overlapping joints and intumescent sealant on all gaps of both layers. Then skimmed. Floor is RW5, TPM sheet, 1 layer T&G, acoustic rubber mat, then another layer of T&G, then sound deadening underlay, then laminate.

2 sets of external doors with seals (but used internally - they are solid oak with glass to maintain sight lines), internal secondary double glazing. Its pretty quiet now - yes you can still hear it, but its generated about 50db attenuation on a 90db source, which is workable at the volumes I work at.

Very much appreciate you taking the time to reply. I had heard a few people say that there wasn't much to gain by adding resilient bars to an already decoupled structure, but it's reassuring to hear from those who have successfully built studios featuring a decoupled RWAR without them.

Thankfully our builder friend is very trustworthy, and we are ordering in all the materials and paying only for his time... so it does make it all more more the transparent .

He's spend today sealing all the joints in the MLV layer... so I'm off to test it now. Will let you know how it goes!

Mostly very happy (pleased and relieved to report) at initial test before plasterboarding.

Very loud drumming was almost inaudible when standing right next to the two walls that border directly onto the pavement outside, and our rear neighbour's driveway (it's a corner house).

Understandably there was more leakage through the only wall that contains windows, though this was only really noticeable in our back yard, and not so much on the street or in our next door neighbour's yard which is good. We are awaiting another set of windows for internal glazing so hopefully this should improve that weak spot a little.

What was perplexing and disappointing, however, is that when we went inside our neighbour's outbuilding, the leakage was worse there than from the wall that has windows into our back yard. We don't share a party wall - there is a gap of a few centimetres between the brick outer skin of our building and theirs, and the only shared thing is a ridge tile, which I don't imagine is the problem. Confused!

SH198 wrote:and the only shared thing is a ridge tile, which I don't imagine is the problem. Confused!

This just shows how important small details are in soundproofing. Any hard coupling between layers will dramatically reduce the soundproofing effectiveness so, if that ridge tile is well cemented into both buildings it could easily be transmitting vibrations from one to the other. I also notice that your ceiling construction is lighter so is likely to be less soundproof than the walls so more sound could be reaching the roof.

SH198 wrote:and the only shared thing is a ridge tile, which I don't imagine is the problem. Confused!

This just shows how important small details are in soundproofing. Any hard coupling between layers will dramatically reduce the soundproofing effectiveness so, if that ridge tile is well cemented into both buildings it could easily be transmitting vibrations from one to the other. I also notice that your ceiling construction is lighter so is likely to be less soundproof than the walls so more sound could be reaching the roof.

Darn it! I'm not sure what we could do about the ridge tile. Removing it doesn't seem like an option.

In terms of ceiling construction of the initial building, yes I suppose lighter construction as concrete roof tiles would not have the equivalent mass of a brick/breeze-block cavity wall. However in the ceiling of our RWAR (decoupled from the actual roof) we have got 125mm of Rockwool vs. 100mm in the walls...

SH198 wrote:In terms of ceiling construction of the initial building, yes I suppose lighter construction as concrete roof tiles would not have the equivalent mass of a brick/breeze-block cavity wall. However in the ceiling of our RWAR (decoupled from the actual roof) we have got 125mm of Rockwool vs. 100mm in the walls...

Rockwool does very little to prevent sound transmission - its purpose is to prevent sound bouncing around in the cavities by reducing reflections. I've also realised that you haven't mentioned what type of Rockwool you are using. There's a big difference between Rockwool loft insulation and RWA45 - hopefully you are using the latter (or something very similar).

The plasterboard is going to be your main source of soundproofing for the roof as you need a certain amount of ventilation under the tiles which limits their effectiveness as far as soundproofing is concerned.

zenguitar wrote:The problem with General Builders is that they work in a culture where it is the norm to cut corners. They really do have to work the margins to make a profit, so it is very tempting for them to use, for example, 10 sheets of x where 10 and a half sheets are required to do the job.

Rubbish and I take offense. I really hate to bash you over this though I must say, I am disappointed that such an ordinarily erudite and eloquent man should fall to such slanders!

I still love you man.

To the OP - any way you can discretely, without compromising anything, decouple the roof tile? An expansion gap of some sort?

zenguitar wrote:The problem with General Builders is that they work in a culture where it is the norm to cut corners. They really do have to work the margins to make a profit, so it is very tempting for them to use, for example, 10 sheets of x where 10 and a half sheets are required to do the job.

Rubbish and I take offense. I really hate to bash you over this though I must say, I am disappointed that such an ordinarily erudite and eloquent man should fall to such slanders!

I still love you man.

To the OP - any way you can discretely, without compromising anything, decouple the roof tile? An expansion gap of some sort?

You forget that I am in a different country in a different continent. Rest assured that my comment was entirely factual and no slander was involved. Love you too man

SH198 wrote:I've also realised that you haven't mentioned what type of Rockwool you are using. There's a big difference between Rockwool loft insulation and RWA45 - hopefully you are using the latter (or something very similar).

The plasterboard is going to be your main source of soundproofing for the roof as you need a certain amount of ventilation under the tiles which limits their effectiveness as far as soundproofing is concerned.

We're using a combination of RW5 and RW3. There is 75mm of RW3 between the rafters, and in the floating ceiling there's 50mm of RW5 and another 75mm of RW3...

SH198 wrote:Perhaps we should try an extra plasterboard layer on the ceiling?

You definitley should do this (with green glue)

Provided the ceiling joists are strong enough!

As I mentioned before, a multiple layer construction using different types of plasterboard for each layer is probably better than two layers of the same type of plasterboard. Many years ago the BBC found that a layer of fibreboard with two layers of plasterboard was more effective than just plasterboard but nowadays Green Glue seems to perform a similar function to the fibreboard by giving the structure some compliance.